Process of making printing-plates.



' UNITE STATES PATENT OFFICE.

JACOB ENGELHARDT, OF NEW YORK, N. Y., ASSIGNOR OF TWO-THIRDS TO LOTHARE. SOHWEIZER AND HARRY NEUBER, OF NEW YORK, N. Y.

PROCESS OF MAKING PRINTING-PLATES.

Specification of Letters Patent.

Patented Oct. 3, 1905.

Application fil d August 6, 1901. Renewed August 18, 1904:. Serial No.221,282.

Making Printing-Plates, of which the follow-' ing is a specification.

The object of my invention is to provide certain new and usefulimprovements in the production of printing-plates for reproducingpictures, prints, and similar work, whereby the cost in producing suchplates is vastly reduced and an entirely new result is obtained.

In order that my invention may be fully understood, it will be necessaryfor me to previously explain the methods of producing printing-platesheretofore by hand and by the light process. By the light process theso-called half-tone plates were produced, and to make such a plate theplate or stone was first rendered sensitive by applying a coating ofsensitive asphaltum upon the stone. For applying the asphaltum in theusual manner it was dissolved in chloroform, benzin, ether, &c., andfloated on the plate, and a screenplate was then placed between thenegative and the prepared surface of the stone and the same exposed tolight, and wherever the light acted on the asphaltum the solubility ofthe latter was destroyed, and of course as the light had to pass throughthe screen the surface of the plate was completely covered with smalldots. The plate was then washed with turpentine, the soluble partsremaining. The plate was then etched, and of course the etching-fluidhad no effect wherever the asphaltum remained. The plate obtained was aso-called half-tone plate and produced dots throughout its surface onthe parts that were to print practically white, as well as on the partsto print deeper tints.

Plates are also made by hand and are known as stipple-plates, in whichlithographic ink is applied by a skilled artist direct on the stone bymeans of a pen. The stipple-plates do not have any dots on the partsthat are to be printed white, as in a half-tone plate, and as the shadesdeepen the number and size of the dots increase.

In producing a printing-plate according to my new and improved methodthe plate or stone is first ground off and cleaned and polished to ahigh degree, and it is then provided With an extremely fine grain on itssurface in any suitable manner. I now apply a layer of dissolvedsensitized asphaltum by means of a gelatin roller. The asphaltumdissolved in fatty oils or etheric oils cannot be used, because whendissolved in fatty oil the asphaltum dries slowly and spreads to such adegree that all the interstices of the grain in the plate are filled andthe etheric oils are so volatile that they render uniform spreadingimpossible. It is mostessential, however, that such spreading should beabsolutely uniform. By dissolving the asphaltum in nitrobenzene it canbe spread uniformly upon the grained surface by means of a roller andwithout filling the grain. This plate is then exposed to light through anegative, the light passing directly to the sensitive plate without theuse of a screen-plate. Wherever the light strikes the asphaltum ontheplate, the solubility of the asphaltum is destroyed, as usual, andwhere no light strikes it it remains soluble. When the asphaltum is dry,the soluble parts are washed off with turpentine and then the plate isetched, and a stipple-plate is thus obtained by the photographic-lightprocess in contradistinction to a half-tone plate, as described above.

My improved plate has a grain, as stated, and as the dissolved asphaltumdoes not fill up and close the interstices between the grain whendissolved in nitrobenzene it can be easily removed by washing the platewith turpentine. If, on the other hand, the asphaltum is floated on, ason half-tone plates, and not applied by means of a gelatin roller, allthe interstices of the grain are filled, and exposing the sensitive filmto light through a negative Without the use of a screen would notproduce a printing-plate that could be used.

In order to produce a grain-plate direct from the negative, thedissolved asphaltum must be applied by means of a roller, and so far Ihave found that only when dissolved in nitrobenzene can the asphaltum beapplied by means of a roller.

I thus produce by the light process a plate which is as clearlydistinguished from the half-tone plate made by means of a screen as thehand stipple-plate is distinguished from such half-tone plates.

Having described my invention, what I claim as new, and desire to secureby Letters Patent, is

The process of producing printing-plates from negatives by the action oflight, consisting in rolling a substance sensitive to light upon thegrained surface of a plate, whereby the sensitized coating is appliedmerely to the high portions of the grain in such a manner as not to [illthe interstices and the depressed portions subjecting the layer ofsensitized substance which has thus been transferred upon the plate. tolight, directly through a negative, removing the soluble sensitizedsubstance from the plate after the exposure to light, and then etchingthe plate, substantially as set I5 forth.

In testimony whereof I aflix my signature.

J ACOB ENGELHARDT.

In presence of BENJAMIN \VoLFF, ARTHUR LANDAUER.

